The purpose of this proposal is to study in vitro and in vivo the effectiveness of UV-B irradiation on mouse and human bone marrow stem cells to permit full engraftment and differentiation without chronic immunosuppression and to prevent GVHD in several animal models. We will determine engraftment and completeness of immunologic recovery, both cell mediated and antibody mediated using various in vitro and in vivo assays. The outlined experiments are based on preliminary systematic studies using UV-B irradiation to alter bone marrow immunogenicity and to abrogate graft-vs-host disease without chronic immunosuppression. Since bone marrow transplantation has increasingly become a mainstay of therapy for a variety of hematologic, metabolic and oncologic disorders and since its use may offer a means to induce allo-specific tolerance in adult recipients to solid organ grafts, the proposed studies are highly significant and important. the aim of these detailed studies are to prevent GVHD and circumvent marrow graft rejection or lack of engraftment with pretreatment of the bone marrow inoculum with ultraviolet B (UV-B) irradiation and thus induce permanent allograft acceptance in adult animals. We plan to determine the mechanism of UV-B prevention of GVHD with particular emphasis on the UV-B effect on phenotypic and functional cell alteration of the inoculum in several strains of mice as well as in in vitro studies of human bone marrow. We plan to examine the effect of UV-B on human stem cells, obtained from cord blood or from cadaveric organ donors both in vitro, and particularly in an in vivo model of severe combined immunodeficiency (SCID). Data from these experiments should provide valuable information on immune response of human lymphohematopoietic precursor cells following UV-B irradiation of marrow or cord blood derived stem cells. Studies in rodents, particularly those in the SCID mouse, will form the basis of future studies on the use of UV-B treated bone marrow in cynomolgus monkey model of autologous and allogeneic bone marrow transplantation in preparation for clinical bone marrow transplantation and allogeneic organ transplantation. bone marrow transplantation in adults without the risk of GVHD with rapid engraftment and immunolymphohematopoietic reconstitution without chronic immunosuppression is feasible, relatively simple, and highly effective based on our preliminary studies. Implications of the proposed studies for treatment of hematologic, oncologic, and immune deficiency diseases, as well as organ transplantation may be incalculable.